Diabetes Mellitus: A Fundamental and Clinical Text
3rd Edition
© 2004 Lippincott Williams & Wilkins
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66
Fatty Acids and Insulin Resistance
Guenther Boden
Excessive accumulation of body fat (obesity) and dietary fat intake are both associated with insulin resistance (1,2) (defined here as inhibition of insulin-stimulated total-body glucose uptake). The fact that insulin resistance increases with weight gain and decreases with weight loss (3,4,5) indicates that fat accumulation is not only associated with insulin resistance but in fact causes insulin resistance. Exactly how this happens, however, is not clear. A likely mechanism involves release of one or more messengers originating from the adipose tissue (or from ingested fat) that inhibit insulin action on skeletal muscle and/or the liver. Several candidates for such a role have been proposed, including leptin (6), tumor necrosis factor-α (TNF-α) (7), resistin (8), and free fatty acids (FFAs) (9).
Leptin, the ob gene product, is a peptide produced by adipocytes (10). Its primary effects appear to be on receptors in the hypothalamus, where it is involved in appetite regulation (11). Reports on peripheral effects of leptin have been contradictory. For instance, leptin has been reported to decrease insulin action in rat adipocytes (12), to increase insulin action in C2C12 myotubes (13), and not to have any direct effects on glucose transport in skeletal muscle and adipocytes of rodents (14). Thus, it remains uncertain whether the increased blood leptin levels commonly seen in obese subjects cause insulin resistance.
The inflammatory cytokine TNF-α is overexpressed in adipose tissue of obese, insulin-resistant rodents and humans (7). It has been proposed to play a major role in the pathogenesis of insulin resistance based in part on the observation that TNF-α can produce insulin resistance in cultured 3T3-L1 fat cells and in L6 myotubes (7,15,16). However, several findings suggest that TNF-α is not a major contributor to the insulin resistance associated with obesity. First, neutralization of circulating TNF-α with antibodies had no effect on insulin action (17). Second, incubation of rat muscle with TNF-α for up to 8 hours had no effect on insulin-stimulated glucose uptake (18). Third, total absence of TNF-α in TNF-α knockout mice did not prevent development of insulin resistance in mice in which obesity was induced by thioglucose (19). Also, it is possible that effects of TNF-α on insulin-stimulated glucose uptake may be mediated, at least in part, by fatty acids, because TNF-α has been shown to be lipolytic (20).
Resistin, a novel protein secreted by adipocytes, has also been proposed as a link between obesity and insulin resistance (8). A subsequent report showing that resistin expression was decreased in white adipose tissue of several animal models of obesity and that peroxisome proliferator activator-γ agonists (which decrease insulin resistance) increased resistin expression (21) has cast doubt on this notion.
Here I review the evidence that in humans, FFAs are the most likely link between obesity and insulin resistance. The evidence can be summarized as follows:
  • Plasma FFA levels are usually elevated in obesity (22,23). The reasons for this are not entirely clear but may include increased FFA release from the enlarged adipose tissue mass (with rates of lipolysis from individual fat cells either normal or increased) or reduced FFA clearance (24,25).
  • Increased plasma FFA levels cause acute as well as chronic insulin resistance in skeletal muscle and in the liver (Fig. 66.1).
Free Fatty Acids and Peripheral (Muscle) Insulin Resistance
Acute elevations of plasma FFA concentrations to between 1,000 and 1,500 μM in healthy volunteers or in patients with type 2 diabetes mellitus (DM) did not affect glucose uptake if insulin was kept at basal concentrations (26,27,28,29). This suggested that elevated plasma FFA levels did not interfere with basal (i.e., non–insulin-stimulated) glucose uptake. In contrast, acute elevations of plasma FFAs to between 700 and 1,500 μM (produced by intravenous infusion of heparinized triglyceride emulsions) inhibited total-body glucose uptake (>80% of which is in skeletal muscle) stimulated by insulin levels in the postprandial range (400–600 pM) in healthy men and women (30,31,32,33), patients with type 2 DM (29), and healthy pregnant women (34). Frias et al., however, recently reported that at higher insulin levels (∼1,000 pM) and lower lipid infusion rates, development of insulin resistance could only be shown in men but not in women (35). The physiologic importance of this gender difference remains to be established. Of note is that the FFA-induced insulin resistance develops only 3 to 4 hours after the start of the lipid infusions (30,31), disappears approximately 4 hours after return of plasma FFAs to normal levels (30), and is dose dependent (Fig. 66.2).
Plasma FFA levels are chronically elevated in obesity. Thus, to qualify as a link between obesity and insulin resistance, FFAs
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need to have chronic effects on insulin-stimulated glucose uptake. That FFAs do indeed have such chronic effects was supported by the demonstration that overnight lowering of plasma FFAs with acipimox, a long-acting and potent antilipolytic agent, in obese subjects with or without type 2 DM, approximately doubled their insulin-stimulated glucose uptake (33). This indicated that the elevated plasma FFA levels in these subjects had chronically inhibited insulin sensitivity, which improved on lowering of the FFA levels.
Figure 66.1. Proposed mechanism of obesity-induced insulin resistance. Excessive fat accumulation (obesity) is associated with elevated plasma free fatty acid (FFA) levels that cause insulin resistance in skeletal muscle and in the liver. Other putative but less well established mediators of obesity-induced insulin resistance are leptin, tumor necrosis factor-α, and resistin.
The cellular location of the fat-mediated inhibition of insulin-stimulated glucose uptake has been investigated. The results indicated that elevation of plasma FFA levels produced a transport or phosphorylation (hexokinase) defect (29) (the methods used did not permit differentiation between these two possibilities). This conclusion was based on the observation that rates of insulin-stimulated glucose uptake, glycogen synthesis, and glycolysis were all reduced to similar extents after fat plus heparin infusions (Fig. 66.3). Subsequently, Dresner et al. (36) proposed that the FFA-mediated defect was principally at the level of glucose transport, based on their observation that intracellular glucose (measured with 13C nuclear magnetic resonance spectroscopy) did not increase during FFA-mediated inhibition of insulin-stimulated glucose uptake (which it should have if the block had been at the hexokinase level).
After 4 to 6 hours of plasma FFA concentrations greater than 500 μM, muscle glycogen synthase activity decreased, indicating development of a second FFA-induced defect (31) (Fig. 66.4).
A third defect, namely, FFA-mediated inhibition of carbohydrate oxidation, which was first reported by Randle et al. (37) in rat hearts and diaphragms, develops much earlier than the other two defects (Fig. 66.4). This defect, however, was unlikely to produce insulin resistance because glucose uptake was not impaired during the initial 3 to 4 hours of lipid/heparin infusion when carbohydrate oxidation was already severely inhibited (30,31). This suggests that carbons that have entered the glycolytic pathway but cannot be oxidized [because of an FFA-produced increase in acetyl-coenzyme A and the ensuing inhibition of pyruvate dehydrogenase (38)] are shunted into nonoxidative glycolysis (lactate/alanine production) (29).
Figure 66.2. Effect of plasma free fatty acids (FFA) on insulin-stimulated glucose uptake. Euglycemic (∼4.7 mM) hyperinsulinemic (∼420 pM) clamping was performed in healthy volunteers for 6 hours. High levels of plasma FFA were produced by infusion of triglycerides (0.3 mmol/min) plus heparin (0.4 U/kg/min); intermediate plasma FFA levels were produced by infusion of triglycerides without heparin, and low FFA levels by infusion of saline only. Data are means ± SE. The inhibition of insulin-stimulated glucose uptake became statistically significant approximately 3.5 hours after the start of the lipid infusion. *p < 0.05; **p < 0.01, comparing high with low FFA. (From
Boden G, Chen X, Ruiz J, et al. Mechanisms of fatty acid-induced inhibition of glucose uptake. J Clin Invest 1994;93:2438
, with permission.)
Hence, these data did not support that part of the Randle glucose–fatty acid cycle hypothesis (37) that proposes that FFA oxidation inhibits the rate of glycolysis (through an increase in cytosolic citrate inhibiting phosphofructokinase-1 activity), which in turn inhibits glucose uptake (by suppressing hexokinase activity). Rather, the human data suggest that FFAs primarily inhibit glucose uptake without first affecting glycolysis.
Mechanisms
The long delay (3–4 hours) between the increase in plasma FFAs and the appearance of insulin resistance gave rise to the notion that FFAs must be esterified inside muscle cells to cause insulin resistance. This hypothesis was supported by studies in
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animals and humans that demonstrated a close relationship between muscle fat content and insulin resistance (39,40,41). It was further supported by the demonstration that transgenic mice with muscle-specific overexpression of lipoprotein lipase had an approximately threefold increase in muscle triglyceride content and were insulin resistant (42). Moreover, it was shown (with 1H nuclear magnetic resonance spectroscopy) that increases in plasma FFA levels resulted (within ∼4 hours) in an increase in intramyocellular triglyceride content that occurred concurrently with the onset of insulin resistance (43).
Figure 66.3. Effects of elevated plasma free fatty acid (FFA) levels on rates of glucose uptake (GRd), glycogen synthesis (GS), and glycolysis (GLS) in patients with type 2 diabetes mellitus (NIDDM) during hyperinsulinemic (∼900 pM) isoglycemic (∼11 mM) clamping, and in nondiabetic control subjects during euglycemic hyperinsulinemic (∼500 pM) clamping. Total length of bars represents insulin-stimulated GRd, GS, or GLS, set as 100%. The dark-shaded parts of the bars represent insulin-stimulated GRd, GS, or GLS after 4 hours of elevated plasma FFA (∼1,200 mM in NIDDM, ∼600 mM in controls). FFA inhibited insulin-stimulated GRd, GS, and GLS similarly in patients with NIDDM and normal control subjects, regardless of insulin and FFA levels. ▪, after fat infusion; ([light shade square]), after saline infusion. (From
Boden G, Chen X. Effects of fat on glucose uptake and utilization in patients with non-insulin-dependent diabetes. J Clin Invest 1995;96:1261
, with permission.)
The finding that the development of FFA-mediated insulin resistance was in some way related to accumulation of intramyocellular triglyceride did not prove, however, that insulin resistance was caused by intramyocellular triglyceride. The latter is believed to be only a marker for biochemical signals that accumulate during the synthesis (or breakdown) of intramyocellular triglyceride. Such signals could include increases in cytosolic concentrations of long-chain acyl-coenzyme A or diacylglycerol, metabolites that are known to increase in muscle when plasma FFA levels are elevated, and which are involved in the synthesis of triglyceride. Both long-chain acyl-coenzyme A and diacylglycerol activate protein kinase C (PKC) (44,45,46), a serine/threonine kinase that can inhibit the action of insulin by serine phosphorylation (leading to decreased tyrosine phosphorylation) of the insulin receptor and insulin receptor substrate (IRS)-1 (47,48,49). In fact, it has recently been shown in healthy volunteers that acutely increasing plasma FFA levels (from around 400 to 800 μM) increased muscle diacylglycerol concentration and muscle membrane–associated PKC activity approximately fourfold (50). These changes occurred together with development of insulin resistance. Similarly, Griffin et al. (51) demonstrated blunting of insulin-stimulated tyrosine phosphorylation of IRS-1 and a fourfold increase in active (membrane-bound) PKC protein in lipid/heparin-infused rats. In rats, it was the PKC θ isoform that was activated by FFAs (51), whereas in human muscle, the PKC isoforms β II and δ (50) were activated. Together with data showing that FFA-induced insulin resistance can be prevented by inactivation of another serine kinase, IκB kinase-β (IKK-β) (52,53,54), these results support the concept that FFAs can activate PKC, IKK, or still other serine/threonine kinases in muscle, which then may interfere with insulin signaling via serine phosphorylation of the insulin receptor or IRS-1.
Figure 66.4. Defects of glucose utilization produced by free fatty acids (FFA). The inhibition of carbohydrate (CHO) oxidation (defect 1) is the earliest demonstrable defect. It develops immediately after start of lipid infusions, but does not inhibit insulin-stimulated glucose uptake or glycolysis. The inhibition of glucose transport or phosphorylation (defect 2) develops after 3 to 4 hours, whereas inhibition of glycogen synthesis (defect 3) develops after 4 to 6 hours of high FFA. E.C., extracellular; I.C., intracellular.
Other less well established ways by which fatty acids may cause insulin resistance include FFA-induced changes in membrane fluidity (55), FFA-mediated inhibition of glucose transporter (GLUT)-4 transcription or message stability (56), or activation of the hexosamine pathway (57).
Free Fatty Acid and Hepatic Insulin Resistance
Several studies have shown that increasing plasma FFAs will partially inhibit insulin-induced suppression of endogenous glucose production (EGP) (i.e., cause hepatic insulin resistance) (31,58,59,60). Whether gluconeogenesis (GNG) or glycogenolysis (GL) or both were responsible for this FFA-mediated insulin resistance has recently been investigated in healthy volunteers in whom euglycemic-hyperinsulinemic clamping was performed either with simultaneous intravenous infusion of lipid plus heparin (to increase plasma FFAs) or without lipid/heparin infusions (to decrease plasma FFAs) (61). In this study, GNG decreased only modestly, regardless of whether FFAs were high or low. On the other hand, GL was rapidly and completely suppressed by insulin infusion, confirming two recent reports, one in diabetic and nondiabetic subjects by Gastaldelli et al. (62), the other in dogs by Edgerton et al. (63). When insulin was coinfused with fat, GL decreased at the same rate as when insulin was infused alone, but only during the initial 2 hours. After 2 hours, GL increased and reached almost preinfusion levels after 4 hours (Fig. 66.5). These results indicated that the FFA-induced attenuation of insulin suppression of EGP (i.e., hepatic insulin resistance) was caused primarily by inhibition of
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insulin suppression of GL. They also suggested that elevated plasma FFAs in patients with type 2 DM may be responsible, at least in part, for the relative (in relation to insulin levels) or absolute elevations in EGP in these patients.
The biochemical mechanisms involved in FFA-induced hepatic insulin resistance are not known but may be similar to those responsible for FFA-induced insulin resistance in muscle. This was suggested by the similar time course and by a recent report by Lam et al. (64) in rats showing that lipid/heparin-induced hepatic insulin resistance was associated with a progressive increase in PKC δ activation in the liver.
Figure 66.5. Effects of euglycemic-hyperinsulinemic clamping with (•, n = 6) and without (○, n = 7) lipid/heparin infusion on endogenous glucose production (EGP), gluconeogenesis (GNG), and glycogenolysis (GL). *p < 0.05; **p < 0.001 compared with basal values. †p < 0.05, 120- and 180-minute vs. 240-minute values. (From
Boden G, Cheung P, Stein P, et al. FFA cause hepatic insulin resistance by inhibiting insulin suppression of glycogenolysis. Am J Physiol 2002;283:E12
, with permission).
Free Fatty Acids and Insulin Secretion
FFA-induced insulin resistance needs to be compensated for, either by hyperinsulinemia or by hyperglycemia, or both, to ensure normal glucose uptake into the major insulin-sensitive tissues (i.e., muscle, liver, and adipose tissue). Compensation by hyperinsulinemia is preferable to compensation by hyperglycemia because the latter results in DM. Fortunately, FFAs are strong insulin secretagogues. Acute stimulation of insulin secretion by FFAs has been well established in humans and animals (65,66). It is also noteworthy that in fasted rats, FFAs have been demonstrated to be essential for glucose- and non–glucose-stimulated insulin secretion during refeeding (67). In vitro results, however, have been contradictory. On the one hand, it has been reported that prolonged exposure of isolated rat islets or perfused rat pancreas to elevated FFA levels produces a biphasic insulin response, an initial stimulation for approximately 3 to 6 hours followed by severe inhibition (lipotoxicity) after 24 hours (68,69). On the other hand, another study showed that even in vitro, FFAs stimulated insulin secretion for as long as 72 hours (70). The reason for these discrepant in vitro findings are not clear. In vivo, rather than being lipotoxic, prolonged (48-hour) elevation of plasma FFA levels has been shown to potentiate glucose-stimulated insulin secretion in healthy subjects (71) (Fig. 66.6). It appears unlikely, therefore, that physiologically elevated plasma FFA levels (<1.5 mM) are “lipotoxic” to β-cells, at least not in humans. If they were, type 2 DM would be expected to develop in all obese subjects with elevated plasma FFA levels, when in fact only approximately 20% of obese subjects ever become diabetic.
The fact that FFAs can potentiate glucose-stimulated insulin secretion for as long as 48 hours does not, of course, prove that the chronically elevated plasma FFA levels seen in obese subjects have the same effect. Results of two studies have indicated, however, that FFAs have chronic stimulatory effects on insulin secretion. In the first study, postabsorptive plasma FFA levels were acutely lowered with nicotinic acid in nondiabetic and diabetic subjects. This resulted in an approximately 30% decrease in basal insulin secretion in both groups (72) (Fig. 66.7). In the second study, plasma FFAs were lowered overnight by 60% to 70% with acipimox, a long-acting nicotinic acid analogue, in obese subjects who had either impaired glucose tolerance or type 2 DM, and in nondiabetic control subjects. This resulted in an approximately 50% decrease of insulin levels in all three groups (33). Together, these studies demonstrated that basal plasma FFA levels supported 30% to 50% of basal insulin levels.
Free Fatty Acids and Type 2 Diabetes Mellitus
Quantitative assessment of FFA-induced insulin resistance in nondiabetic subjects suggests that for every 100 μM increase in plasma FFAs, insulin resistance increases by approximately 5% to 10% (73). Because FFA-induced insulin secretion increased to a similar degree, FFA-induced insulin resistance is completely or nearly completely compensated for by FFA-induced insulin secretion. A small resistance–secretion deficit, if indeed there was one, could easily be compensated for by a small increase
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in blood glucose concentration, which would remain well within normal limits. Thus, in obese, insulin-resistant subjects, who are not predisposed to develop type 2 diabetes (i.e., in ∼ 80% of obese people), most or all of their compensatory hyperinsulinemia seems to be driven by elevated plasma FFAs. The situation is different in patients with type 2 DM for several reasons. First, their FFA-induced peripheral and hepatic insulin resistance is not fully compensated because these patients secrete less insulin in response to FFAs than nondiabetic control subjects (partial lipid blindness) (74,75). Second, patients with type 2 DM have a well-recognized problem with glucose-stimulated insulin secretion (partial glucose blindness). Thus, they need a much larger increase in blood glucose than nondiabetic subjects to compensate for their FFA-induced insulin resistance. A further compounding factor is that patients with type 2 DM have insulin resistance that is unrelated to FFAs in addition to their FFA-induced insulin resistance (29). This is illustrated in Fig. 66.8, which shows that under conditions of euglycemia and comparable low plasma FFAs (<100 μM), insulin-stimulated glucose uptake is approximately two times higher in nondiabetic control subjects than in obese patients with type 2 DM, indicating that FFAs could account for no more than approximately 50% of insulin resistance in these diabetic patients.
Figure 66.6. Effect of prolonged elevation of plasma free fatty acids (FFA) on insulin secretory rates (ISR). Lipid plus heparin or saline was infused for 48 hours in six healthy volunteers during hyperglycemic (∼8.8 mM) clamping. Elevated plasma FFAs were associated with increased ISR throughout the 48-hour study. Δ, lipid; •, saline. (From
Boden G, Chen X, Rosner J, et al. Effects of a 48-hour fat infusion on insulin secretion and glucose utilization. Diabetes 1995;44:1239
, with permission.)
Figure 66.7. Effects of nicotinic acid (NA; 100–150 mg every 30 minutes for 4 hours) on plasma free fatty acid (FFA) levels, insulin, and insulin secretion rates (ISR) in type 2 diabetic patients during euglycemic (EU) and isoglycemic (ISO) clamping, and in nondiabetic control subjects during euglycemic clamping. Data are means ± SE. *p < 0.03, basal values (mean of values from -30 to 0 minutes) versus values during nicotinic acid (mean of values from 180 to 240 minutes). (From
Boden G, Chen X, Iqbal N. Acute lowering of plasma fatty acids lowers basal insulin secretion in diabetic and nondiabetic subjects. Diabetes 1998;47:1609
, with permission.)
On the basis of these observations, we have proposed that obese subjects, who are genetically predisposed to development of type 2 DM and have elevated plasma FFA levels, are partially “lipid blind,” and because of that have a degree of uncompensated insulin resistance that will grow larger over time (probably
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because of an inherited β-cell defect). At the same time, they are also acquiring impaired β-cell responses to changes in plasma glucose (“glucose blindness”). The result is that ever-larger increases in plasma glucose concentrations are needed to compensate for the FFA-mediated hepatic and peripheral insulin resistance. This will eventually result in overt DM (Fig. 66.9).
Figure 66.8. Insulin-stimulated glucose uptake (GRd) at comparable low plasma free fatty acids (FFA; <100 mM) and euglycemia in diabetic and nondiabetic subjects. Shown is insulin-stimulated GRd before ([light shade square]) and after 4 hours of euglycemic (∼4.8 mM) hyperinsulinemic (∼500 pM) clamping (□) in seven patients with type 2 diabetes mellitus and six nondiabetic control subjects. Preclamp glucose uptake could not be obtained in the diabetic patients because insulin was infused to lower their blood glucose concentrations into the normal range. Plasma FFAs were less than 100 mM in both groups, whereas insulin-stimulated GRd was approximately twofold higher in nondiabetic than in diabetic subjects (30 vs. 58 μmol/kg fat free mass, p < 0.01). Triglyceride plus heparin infusion (▪) decreased insulin-stimulated GRd by approximately 50% in diabetic and nondiabetic individuals. EU, euglycemia; FFM, fat free mass. (Adapted from
Boden G, Chen X. Effects of fat on glucose uptake and utilization in patients with non-insulin-dependent diabetes. J Clin Invest 1995;96:1261
, with permission.)
Free Fatty Acids and Atherosclerosis
The chronic insulin resistance of obesity is associated with several cardiovascular risk factors, including hypertension, dyslipidemia, abnormal blood coagulation, and fibrinolysis (76). The molecular/biochemical basis of the connection between insulin resistance and these risk factors remains largely unknown. Recent data have suggested, however, that acute FFA-induced development of insulin resistance is associated with activation of nuclear factor β (NFβ) (50). The NFβ pathway is a major proinflammatory pathway, and inflammatory processes are now recognized to play a pivotal role in the pathogenesis of coronary artery disease (77). Hence, activation of the NFβ pathway by FFAs may be responsible for at least some of the increased prevalence of coronary artery disease in obese patients with type 2 diabetes.
Figure 66.9. Proposed role of free fatty acids (FFA) in the development of type 2 diabetes. In obese subjects with a genetic predisposition for development of type 2 diabetes (e.g., first-degree relatives of patients with type 2 diabetes), high plasma levels of FFAs cause insulin resistance (heavy black lines) that cannot be completely compensated by increased insulin secretion (broken lines). Plasma glucose levels increase as a result of the partially uncompensated insulin resistance. The resulting hyperglycemia increases glucose uptake by mass effect and by enhancing insulin secretion. (From
Boden G. Free fatty acids—the link between obesity and insulin resistance. Endocr Pract 2001;7: 44
, with permission.)
Summary
Physiologic elevations of plasma FFA levels cause peripheral (muscle) and hepatic insulin resistance, whereas lowering of plasma FFA levels improves peripheral insulin sensitivity in diabetic and nondiabetic subjects. FFA-induced insulin resistance in muscle is produced by defects in insulin-stimulated glucose transport or phosphorylation and in glycogen synthesis that develops over a period of 3 to 6 hours. Development of these defects is temporally associated with accumulation in muscle cells of diacylglycerol and activation of PKC βII and δ. In nondiabetic, obese subjects, FFA-induced insulin resistance is fully or nearly fully compensated for by FFA-mediated stimulation of insulin secretion. In patients with type 2 DM, FFA-mediated stimulation of insulin secretion is impaired (partial β-cell lipid blindness); hence, FFA-induced insulin resistance needs to be compensated for by hyperglycemia and hyperinsulinemia.
Acknowledgments
This work was supported by National Institutes of Health Grants R01-DK58895, R01-AG-15363, and 2M01-RR-00349 (General Clinical Research Center Branch of the National Center for Research Resources) and a Mentor Based Training Grant from the American Diabetes Association.
References
1. Ferrannini E, Natali A, Bell P, et al. Insulin resistance and hypersecretion in obesity. J Clin Invest 1997;100:1166.
2. Pascoe WS, Storlien LH. Inducement by fat feeding of basal hyperglycemia in rats with abnormal beta-cell function: model for study of etiology and pathogenesis of NIDDM. Diabetes 1990;39:226.
3. Sims EAH, Danforth E Jr, Horton ES, et al. Endocrine and metabolic effects of experimental obesity in man. Rec Prog Horm Res 1973; 29:457.
4. Goto Y, Nakayama Y, Yagi T. Influence of the World War II food shortage on the incidence of diabetes mellitus in Japan. Diabetes 1958;7:133.
5. Schliack V. Mangelernahrung und Diabetes Morbiditat. Z Klin Med 1954;151:382.
6. Cohen B, Novick D, Rubinstein M. Modulation of insulin activities by leptin. Science 1996;274:1185.
7. Hotamisligil GS, Spiegelman BM. Tumor necrosis factor: a key component of the obesity-diabetes link. Diabetes 1994;43:1271.
8. Steppan CM, Bailey ST, Bhat S, et al. The hormone resistin links obesity to diabetes. Nature 2001;409:307.
P.985

9. Boden G. Role of fatty acids in the pathogenesis of insulin resistance and NIDDM. Diabetes 1997;46:3.
10. Zhang Y, Proenca R, Maffei M, et al. Positional cloning of the mouse obese gene and its human homologue. Nature 1994;372:425.
11. Caro JF, Sinha MK, Kolaczynski JW, et al. Leptin: the tale of an obesity gene. Diabetes 1996;45:1455.
12. Müller G, Ertl J, Gerl M, et al. Leptin impairs metabolic actions of insulin in isolated rat adipocytes. J Biol Chem 1997;272:10585.
13. Berti L, Kellerer M, Capp E, et al. Leptin stimulates glucose transport and glycogen synthesis in C2C12 myotubes: evidence for a PI 3 kinase mediated effect. Diabetologia 1997;40:606.
14. Zierath JR, Frevert EU, Ryder JW, et al. Evidence against a direct effect of leptin on glucose transport in skeletal muscle and adipocytes. Diabetes 1998;47:1.
15. Kroder G, Bossenmaier B, Kellerer M, et al. Tumor necrosis factor-α– and hyperglycemia-induced insulin resistance. J Clin Invest 1996;97: 1471.
16. Begum N, Ragolia L. Effect of tumor necrosis factor-α on insulin action in cultured rat skeletal muscle cells. Endocrinology 1996;137: 2441.
17. Ofei F, Hurel S, Newkirk J, et al. Effects of an engineered human anti-TNF-α antibody (CDP571) on insulin sensitivity and glycemic control in patients with NIDDM. Diabetes 1996;45:881.
18. Nolte LA, Hansen PA, Chen MM, et al. Short-term exposure to tumor necrosis factor-α does not affect insulin-stimulated glucose uptake in skeletal muscle. Diabetes 1998;47:721.
19. Ventre J, Doebber T, Wu M, et al. Targeted disruption of the tumor necrosis factor-α gene. Metabolic consequences in obese and nonobese mice. Diabetes 1997;46:1526.
20. Van Der Poll T, Romijin JA, Endert E, et al. Tumor necrosis factor mimics the metabolic response to acute infection in healthy humans. Am J Physiol 1991;24:E457.
21. Way JM, Gorgun CZ, Tong Q, et al. Adipose tissue resistin expression is severely suppressed in obesity and stimulated by peroxisome proliferator-activated receptor γ agonists. J Biol Chem 2001;276:25651.
22. Gorden ES. Non-esterified fatty acids in blood of obese and lean subjects. Am J Clin Nutr 1960;8:740.
23. Reaven GM, Hollenbeck C, Jeng C-Y, et al. Measurement of plasma glucose, free fatty acid, lactate and insulin for 24 h in patients with NIDDM. Diabetes 1988;37:1020.
24. Bjorntorp P, Bergman H, Varnauskas E. Plasma free fatty acid turnover in obesity. Acta Med Scand 1969;185:351.
25. Jensen MD, Haymond MW, Rizza RA, et al. Influence of body fat distribution on free fatty acid metabolism in obesity. J Clin Invest 1989; 83:1168.
26. Boden G, Jadali F. Effects of lipid on basal carbohydrate metabolism in normal men. Diabetes 1991;40:686.
27. Saloranta C, Koivisto V, Widen E, et al. Contribution of muscle and liver to glucose-fatty acid cycle in humans. Am J Physiol 1993;264: E599.
28. Piatti P, Monte L, Baruffaldi L, et al. Effects of an acute increase in plasma triglyceride levels on glucose metabolism in man. Metabolism 1995;44:883.
29. Boden G, Chen X. Effects of fat on glucose uptake and utilization in patients with non–insulin-dependent diabetes. J Clin Invest 1995;96: 1261.
30. Boden G, Jadali F, White J, et al. Effects of fat on insulin-stimulated carbohydrate metabolism in normal men. J Clin Invest 1991;88:960.
31. Boden G, Chen X, Ruiz J, et al. Mechanisms of fatty acid-induced inhibition of glucose uptake. J Clin Invest 1994;93:2438.
32. Roden M, Price TB, Perseghin G, et al. Mechanisms of free fatty acid induced insulin resistance in humans. J Clin Invest 1996;17:2859.
33. Santomauro A, Boden G, Silva M, et al. Overnight lowering of free fatty acids with acipimox improves insulin resistance and glucose tolerance in obese diabetic and non-diabetic subjects. Diabetes 1999;48: 1836.
34. Sivan E, Homko CJ, Whittaker PG, et al. Free fatty acids and insulin resistance during pregnancy. J Clin Endocrinol Metab 1998;83:2338.
35. Frias JP, Macaraeg GB, Ofrecio J, et al. Decreased susceptibility to fatty acid-induced peripheral tissue insulin resistance in women. Diabetes 2001;50:1344.
36. Dresner A, Laurent D, Marcucci M, et al. Effects of free fatty acids on glucose transport and IRF-1-associated phosphatidylinositol 3-kinase activity. J Clin Invest 1999;103:253.
37. Randle PJ, Garland PB, Hales CN, et al. The glucose fatty-acid cycle: its role in insulin sensitivity and the metabolic disturbances of diabetes mellitus. Lancet 1963;1:785.
38. Kelley DE, Mokan M, Simoneau J-A, et al. Interaction between glucose and free fatty acid metabolism in human skeletal muscle. J Clin Invest 1993;92:91.
39. Pan DA, Lillioja S, Kriketos AD, et al. Skeletal muscle triglyceride levels are inversely related to insulin action. Diabetes 1997;46:983.
40. Simoneau JA, Colberg SR, Thaete FL, et al. Skeletal muscle glycolytic and oxidative enzyme capacities are determinants of insulin sensitivity and muscle composition in obese women. FASEB J 1995;9:273.
41. Oakes ND, Cooney GJ, Camilleri S, et al. Mechanisms of liver and muscle insulin resistance induced by chronic high-fat feeding. Diabetes 1997;46:1768.
42. Kim JK, Fillmore JJ, Chen Y, et al. Tissue-specific overexpression of lipoprotein lipase causes tissue-specific insulin resistance. Proc Natl Acad Sci USA 2001;98:7522.
43. Boden G, Lebed B, Schatz M, et al. Effects of acute changes of plasma FFA on intramuscular fat content and insulin resistance in healthy subjects. Diabetes 2001;50:1612.
44. Farese RV. Protein kinase C. In: Olefsky J, Taylor SE, LeRoith D, eds. Diabetes mellitus: a fundamental and clinical text. Philadelphia: Lippincott Williams & Wilkins, 2000:239–251.
45. Bronfman M, Morales MN, Orellano A. Diacylglycerol activation of protein kinase C is modulated by long-chain acyl-CoA. Biochem Biophys Res Commun 1988;152:987.
46. Nesher M, Boneh A. Effect of fatty acids and their acyl-CoA esters on protein kinase C activity in fibroblasts: possible implications in fatty acid oxidation defects. Biochim Biophys Acta 1994;1221:66.
47. Chin JE, Dickens M, Tavare JM, Roth RA. Overexpression of protein kinase C isoenzymes alpha, beta I, gamma and epsilon in cells overexpressing the insulin receptor. Effects on receptor phosphorylation and signaling. J Biol Chem 1993;268:6338.
48. DeFea K, Roth RA. Modulation of insulin receptor substrate-1 tyrosine phosphorylation and function by mitogen-activated protein kinase. J Biol Chem 1997;272:31400.
49. Ravichandran LV, Esposito DL, Chen J, et al. Protein kinase C-ζ phosphorylates insulin receptor substrate-1 and impairs its ability to activate phosphatidylinositol 3-kinase in response to insulin. J Biol Chem 2000;276:3543.
50. Itani SI, Ruderman NB, Schmieder F, et al. Lipid induced insulin resistance in human muscle is associated with changes in diacylglycerol, protein kinase C and IB-α. Diabetes 2000;51:2005.
51. Griffin ME, Marcucci MJ, Cline GW, et al. Free fatty acid-induced insulin resistance is associated with activation of protein kinase C θ and alterations in the insulin signaling cascade. Diabetes 1999;48: 1270.
52. Ginsberg BH, Brown TJ, Simon I, et al. Effect of membrane lipid environment on the properties of insulin receptors. Diabetes 1981;30: 773.
53. Kim JK, Kim YJ, Fillmore, et al. Prevention of fat-induced insulin resistance by salicylate. J Clin Invest 2001;108:437.
54. Yuan M, Konstantopoulos N, Lee J, et al. Reversal of obesity- and diet-induced insulin resistance with salicylates or targeted disruption of Ikkbeta. Science 2001;293:1673.
55. Borkman M, Storlien LH, Pan DA, et al. The relation between insulin sensitivity and the fatty-acid composition of skeletal-muscle phospholipids. N Engl J Med 1993;328:238.
56. Long SD, Pekala PH. Regulation of Glut4 gene expression by arachidonic acid: evidence for multiple pathways, one of which requires oxidation to prostaglandin E2. J Biol Chem 1996;271:1138.
57. Hawkins M, Barzilai N, Liu R, et al. Role of the glucosamine pathway in fat-induced insulin resistance. J Clin Invest 1997;99:2173.
58. Ferrannini E, Barrett E, Bevilacqua S, et al. Effect of fatty acids on glucose production and utilization in man. J Clin Invest 1983;72: 1737.
59. Bevilacqua S, Buzzigoli G, Bonadonna R, et al. Operation of Randle’s cycle in patients with NIDDM. Diabetes 1990;39:383.
P.986

60. Fanelli C, Calderone S, Epifano L, et al. Demonstration of a critical role for free fatty acids in mediating counterregulatory stimulation of gluconeogenesis and suppression of glucose utilization in humans. J Clin Invest 1993;92:1617.
61. Boden G, Cheung P, Stein TP, et al. FFA cause hepatic insulin resistance by inhibiting insulin suppression on glycogenolysis. Am J Physiol 2002;283:E12.
62. Gastaldelli A, Toschi E, Pettiti M, et al. Effect of physiological hyperinsulinemia on gluconeogenesis in nondiabetic subjects and in type 2 diabetic patients. Diabetes 2001;50:1807.
63. Edgerton DS, Cardin S, Emshwiller M, et al. Small increases in insulin inhibit hepatic glucose production solely caused by an effect of glycogen metabolism. Diabetes 2001;50:1872.
64. Lam TK, Yoshii H, Haber CA, et al. Free fatty acid–induced hepatic insulin resistance: a potential role for protein kinase C-δ. Am J Physiol 2002;283:E7682.
65. Felber JP, Vanotti A. Effects of fat infusions on glucose tolerance and insulin plasma levels. Med Exp 1964;10:153.
66. Crespin SR, Greenough WB, Steinberg D. Stimulation of insulin secretion by long-chain free fatty acids. J Clin Invest 1973;52:1979.
67. Dobbins RL, Chester MW, Stevenson BE, et al. A fatty acid-dependent step is critically important in both glucose- and non–glucose-stimulated insulin secretion. J Clin Invest 1998;101:2370.
68. Sako Y, Grill VE. A 48-hour lipid infusion in the rat time-dependently inhibits glucose-induced insulin secretion and β-cell oxidation through a process likely coupled to fatty acid oxidation. Endocrinology 1990;127:1580.
69. Zhou Y-P, Grill VE. Long-term exposure of rat pancreatic islets to fatty acids inhibits glucose-induced insulin secretion and biosynthesis through a glucose fatty acid cycle. J Clin Invest 1994;93:870.
70. Bollheimer LC, Skelly RH, Chester MW, et al. Chronic exposure to free fatty acids reduced pancreatic β cell insulin content by increasing basal insulin secretion that is not compensated for by a corresponding increase in proinsulin biosynthesis translation. J Clin Invest 1998;101–109.
71. Boden G, Chen X, Rosner J, et al. Effects of a 48-h fat infusion on insulin secretion and glucose utilization. Diabetes 1995;44:1239.
72. Boden G, Chen X, Iqbal N. Acute lowering of plasma fatty acids lowers basal insulin secretion in diabetic and nondiabetic subjects. Diabetes 1998;47:1609.
73. Boden G. Free fatty acids (FFA), a link between obesity and insulin resistance. Front Biosci 1998;3:d169.
74. Boden G, Chen X. Effects of fatty acids and ketone bodies on basal insulin secretion in type 2 diabetes. Diabetes 1999;48:577.
75. Hirose H, Lee YH, Inman LR, et al. Defective fatty acid mediated β-cell compensation in Zucker diabetic fatty rats. J Biol Chem 1996;271: 5633.
76. Reaven GM. Role of insulin resistance in human disease. Diabetes 1988;37:1595.
77. Ross R. Atherosclerosis—an inflammatory disease. N Engl J Med 1999;34:115.
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